Pine Wilt

Pine wilt is the result of the pine wood nematode (Bursaphelebchus
xylophilus) invading xylem tissue. The nematode is usually transported
from one tree to another via insects. The nematode breeds fairly
rapidly and sometimes in association with bacteria quickly causes
the vascular tissue to plug—killing the tree. It has been
proven that the nematode alone can cause the tree to die. The nematode
feeds on plant tissue or fungal mycelium such as blue stain canker
mycelium. Scots pine is one of the most susceptible and eastern
white pine is one of the most resistant. Other pines fall somewhere
in between. It has also been found in other types of needle evergreens.

Symptoms

Most pines infected in the spring are often dead by late summer – early
fall. Large trees may take two years to die. Vigor of plant does
not seem to have a bearing on which plants become infected. Infected
plants quickly become stunted. Foliage begins to fade to and off
green or slightly yellowish color. Dead needles hang on to the
branches for a long time. On large trees that take two years to
die, the older needles turn yellow first and fall off before the
younger needles turns brown. Sawyer beetles, which are native long
horns, are known to transmit this nematode. The beetles that nest
in dead trees and feed on "healthy" trees are the most
likely to transmit the nematode. One long horn can carry several
thousand nematodes on and in their bodies. The nematode can alter
its development based on whether it is in a dead or drying out
tree or in a tree still somewhat viable. The nematode can take
between four and twelve days to go from egg to adult depending
on temperature. Females lay dozen of eggs over several weeks before
dying themselves.

Dying or dead trees are then not only attacked by longhorns but
also bark beetles and other saprophytic insects. In addition
saprophytic nematodes and predator nematodes can be found on the
dead pines.
Proper identification of the nematodes is important. The nematode
presence does not necessarily prove that they killed the tree.
Research has shown that under certain growing conditions the
pines do not die. Pines under stress are more likely to be killed
by
the pine wood nematode.

Control

Have suspected plants tested. If results are positive, remove
diseased and dead evergreens as soon as possible to reduce breeding
sites
for the insects that transmit the pine wood nematode.